line-log: untangle the -L machinery and make get_commit_action() pure

Makefile

@@ -1256,6 +1256,7 @@ LIB_OBJS += prune-packed.o
 LIB_OBJS += pseudo-merge.o
 LIB_OBJS += quote.o
 LIB_OBJS += range-diff.o
+LIB_OBJS += range-set.o
 LIB_OBJS += reachable.o
 LIB_OBJS += read-cache.o
 LIB_OBJS += rebase-interactive.o
@@ -1533,6 +1534,7 @@ CLAR_TEST_SUITES += u-oid-array
 CLAR_TEST_SUITES += u-oidmap
 CLAR_TEST_SUITES += u-oidtree
 CLAR_TEST_SUITES += u-prio-queue
+CLAR_TEST_SUITES += u-range-set
 CLAR_TEST_SUITES += u-reftable-basics
 CLAR_TEST_SUITES += u-reftable-block
 CLAR_TEST_SUITES += u-reftable-merged

diff.c

@@ -17,6 +17,7 @@
 #include "quote.h"
 #include "diff.h"
 #include "diffcore.h"
+#include "range-set.h"
 #include "delta.h"
 #include "hex.h"
 #include "xdiff-interface.h"

diffcore.h

@@ -9,6 +9,7 @@
 struct diff_options;
 struct mem_pool;
 struct oid_array;
+struct range_set;
 struct repository;
 struct strintmap;
 struct strmap;
@@ -19,17 +20,6 @@ struct userdiff_driver;
  * in anything else.
  */
 
-/* A range [start, end).  Lines are numbered starting at 0. */
-struct range {
-	long start, end;
-};
-
-/* A set of ranges.  The ranges must always be disjoint and sorted. */
-struct range_set {
-	unsigned int alloc, nr;
-	struct range *ranges;
-};
-
 /* We internally use unsigned short as the score value,
  * and rely on an int capable to hold 32-bits.  -B can take
  * -Bmerge_score/break_score format and the two scores are